One of the major problems with conventional hydrogen storage alloys is that upon cycling, the particles of the powdered hydrogen storage alloy tend to break apart upon absorption/desorption cycling. This breaking up or decrepitation can cause problems in the use of hydrogen storage alloys. Previous patents and applications have addressed this problem by container design, compartmentalization of the interior of the containers and internal thermal management systems. Another problem involves the irreversibility of some hydrogen storage in alloys. The present invention minimizes decrepitation by using the nano foam-like structure, which allows for a great reduction in pressure containment requirements and weight of the storage vessel holding the hydrogen storage material. Importantly the present invention does this using materials having proven hydrogen storage capabilities in a nano foam-like structure which gives extra degrees of freedom to gain more hydrogen storage sites, reversibly or otherwise. The present invention also increases the reversibility of hydrogen storage in some alloys. It does so via a unique reticulated foam-like structure formed of nano-scale particulate which solves kinetic issues, storage capacity issues, and cycle-life issues of gas phase hydrogen storage materials. The nano-scale foam has a structural integrity of their own and do not need a substrate to support them. This means that there can be two or three dimensionality of materials that are put into play which increases the number of available hydrogen sites (although substrates can be utilized which have their own wave functions and interact with the wave functions of the elements of the nano-foam). It should be noted that the increased catalytic activity of the present material, due not only to increased surface sites but also to their associated chemistry, leads to improved capacity and kinetics. The present reticulated foam-like structure is also useful beyond just hydrogen storage materials and can improve battery and fuel cell materials (both positive and negative electrodes), as well as making outstanding multi-functional catalytic materials.
The reticulated foam-like structure is fractal in nature and when purposefully broken up into smaller chunks, the nano-scale structure will not fracture. Thus the fractal structure is preserved. The surface area of the reticulated foam-like structure is as great as that of carbon nano-foam. Having fractal configurations the reticulated foam-like structure does not pack together the same as simple particles would.
Hydrogen for use in fuel cells and as a fuel in internal combustion engines is rapidly taking its place as the next major evolution in energy usage. Unfortunately, conventional means of safely and usefully storing hydrogen reversibly are currently very difficult and expensive. Such fuels are now stored in pressurized tanks or liquid form. We have chosen the solid state storage of hydrogen in hydride storage systems. Hydride storage is far safer than compressed hydrogen gas or liquid storage, and safer even than gasoline on an equivalent-energy basis.
In usage, hydrides have weight penalties versus compressed hydrogen. Additionally, the space limitations on motor vehicles require storage to be close to passengers, compounding such safety concerns. These storage limitations penalize not just on-board vehicle storage and vehicle range, but also the capacity for overall transportation and distribution of hydrogen versus gasoline or other existing fuels, and its storage prior to use. These limitations in turn limit where, how efficiently, and how cleanly hydrogen can be produced. For example, hydrogen generation onboard vehicles from methanol or gasoline reformers cuts total emissions only 7-35%, while steam reforming at service stations would reduce emissions by 40%, and remote generation would reduce emissions by 60-70%, given a practical and economical storage method. A better method of both on-board storing, and transporting and distributing, of hydrogen, including pure hydrogen fuel cell vehicles would have a significant and broad positive impact on this emerging new industry. Thus our material inventions in this area have been able to solve capacity, kinetics and lifetime issues of storage of hydrogen in solid state, but also they have enabled the solutions that are capable of solving the infrastructure problem since they can be transported by ordinary means and the hydrogen can be generated by renewable energy resources such as solar energy captured by triple junction photovoltaic devices, or even using conventional non-renewable sources of hydrogen of any kind.
The main problems of hydrogen fueled vehicles which use conventional high pressure storage hydrogen are vehicle range, safety, and hydrogen fuel availability. These problems are all in turn aspects of the problem of hydrogen storage. A hydrogen fueled vehicle system may achieve the same range as a gasoline ICE (a usual target being 380 miles), but 3-5 times the space and possibly far greater weight are required compared to gasoline. The extra space required also adds to real or perceived safety concerns. These space and weight penalties also affect the ease of transportation and distribution of, hydrogen, which in turn makes vehicle range concerns still more sensitive. The space and range limits, and associated safety concerns of high pressure hydrogen, represent the largest negatives for conventional hydrogen fueled vehicles. An all hydrogen vehicle based on the approach of Stanford R. Ovshinsky which uses either a fuel cell or a hydrogen burning internal combustion engine (both of which only require low pressure hydrogen fuel), in conjunction with Ovonic Nickel-Metal Hydride batteries has been proven to provide the range and capabilities needed for such a vehicle. The vehicle uses Ovonic solid state metal hydride storage for the hydrogen fuel supply.
Metal hydrides, in the form of metallic particles, which can also be multi-elemental, are used to store hydrogen in many different sizes and shaped containers. In order to facilitate the charging and discharging of the hydrogen, the metal hydride and, consequently, the container, needs to be cooled or heated. To facilitate good performance of the container (desorption rate, filling time, etc.), the inside of the container requires efficient heat exchange means to improve the charging/discharging kinetics.
Repeated absorption and desorption cycles typically result in the decrepitation of the metal hydride particles. Decrepitation occurs when the expansion of chunks or particles of the hydrogen storage alloy expand due to absorption of hydrogen causes greater stress/strain on the chunks beyond the elastic modulus of the alloy and the chunks fracture into smaller pieces. By virtue of the decrepitation, smaller particles of the alloy will settle due to gravity and a localized increase in packing fraction of the metallic particles is observed. Such increase in packing fraction, coupled with high static friction between particles and with particle expansion during absorption, can, in some cases, potentially create localized stresses on the containment vessel in which the alloy is stored. This localized densification has been successfully addressed by ECD Hydrogen Systems Company. The localized densification has been minimized so that it does not limit lifetime or any other vehicle consideration. The present invention provides another means for solving the localized densification problem which also allows for decreasing the weight of the containment system.
Further, some bulk hydrogen storage alloy materials initially absorb much more hydrogen than can be reversibly released (at useful temperatures). A portion of the initially absorbed hydrogen is “trapped” in storage sites which require a large amount of energy to release the stored hydrogen. The added degrees of freedom designed by the approach of the instant invention can release hydrogen sites that are not fully utilized and which do not normally store or release hydrogen at normal temperatures and pressures. Many of these prior art alloys are so called “room temperature” alloys which store and release hydrogen at temperatures between 20° C. and 30° C. Beneficially these alloys can store 2.5 to over 4 wt. % hydrogen. The approach of the present invention permits utilization of those portions of hydrogen storage that have not heretofore been accessible. A multi-functional foam combined with atomic engineering as achieved in our Ovonic Battery patents, which have enabled the present HEV industry can be extended to and utilized in solid state hydrogen storage materials and systems.
The advancement and enhancement of solid state hydrogen storage is the instant invention. Since hydrogen storage materials are adequate with regard to volumetric storage capacity, the object is to reduce weight and also make packaging of the hydrogen fuel more adaptable for the automobile inductry.